Lubricant compositions

ABSTRACT

Provided are lubricant compositions that exhibit high viscosity index and low Noack volatility. A lubricant composition of the invention comprises: (a) a polyalkylene glycol of formula I: RO-(AO) n -R 1  (I) wherein R, R 1 , and n are as defined herein; and (b) an additive package comprising an anti-oxidant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from provisional application Ser. No. 61/468,615, filed Mar. 29, 2011, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to lubricant compositions comprising a polyalkylene glycol compound and an additive package containing an anti-oxidant. The lubricant compositions exhibit favorable properties, including high viscosity index and low volatility.

BACKGROUND OF THE INVENTION

Lubricant compositions such as engine lubricant oils are composed of base oils and additives. Certain synthetic base oils, such as polyalkylene glycols (PAGs), are characterized by inherent low friction properties and good low and high temperature viscosity properties which promote excellent hydrodynamic film formation between moving parts.

PAG-based lubricants possess a number of advantages compared to conventional mineral oil lubricants, and are increasingly being used by original equipment manufacturers (OEMs) because of their ability to address a growing number of new performance criteria requested by automotive engine design departments.

Notwithstanding their advantages, PAG based lubricants still exhibit some shortcomings. For example, PAGs may exhibit unfavorably high volatility, which can result in increased oil consumption. In addition, the viscosity index of some PAGs may be too low to provide the desired lubrication and fuel efficiency properties. Further, some PAGs may not be oil soluble, resulting in increased costs associated with the process of switching mineral oil based engines to the PAG lubricants. Such costs result from the need to use additional flushing and disposal steps if the PAG is not soluble in the mineral oil.

It would be an advance in the art if new lubricant compositions were developed that exhibit low volatility, high viscosity index or both low volatility and high viscosity index. Lubricant compositions that are also oil soluble would be a further advantage.

BRIEF SUMMARY OF THE INVENTION The invention provides lubricant compositions. A composition according to the invention comprises: (a) a polyalkylene glycol of formula I:

RO—(AO)_(n)—R¹  (I)

wherein R, R¹, and n are as defined below; and (b) an additive package comprising an antioxidant. The lubricant composition has a Noack volatility of 13 percent or less and a viscosity index of at least 165.

The invention also provides a method for lubricating an internal combustion engine. The method comprises providing to the engine a lubricant composition as described herein.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, in one aspect, the invention provides lubricant compositions. The inventors have discovered that the selection of PAGs with specific structural features, such as a short alkyl group at position R¹ in formula I, together with the use of an additive package that contains an anti-oxidant, certain highly desirable properties are achieved. In particular, lubricant compositions are achieved that exhibit both high viscosity index and low volatility. Moreover, in some embodiments, compositions of the invention are also oil soluble, thus facilitating the replacement in engines of conventional mineral oils with such the PAG based lubricants.

A lubricant composition according to the invention comprises: (a) a polyalkylene glycol of formula I:

RO—(AO)_(n)—R¹  (I)

wherein R is C₄-C₂₂ alkyl; AO is independently ethyleneoxy, propyleneoxy, butyleneoxy, or mixtures of two or more thereof; n is 8-16; and R¹ is C₁-C₆ alkyl; and (b) an additive package comprising an anti-oxidant. The lubricant composition has a Noack volatility of 13 percent or less and a viscosity index of at least 165.

Polyalkylene glycols of formula I may be readily prepared by those skilled in the art using well known synthetic techniques. By way of example, a PAG may be formed by known techniques in which an aliphatic alcohol (often called an “initiator”) is reacted with a single 1,2-oxide (ethylene oxide, propylene oxide, or butylene oxide) or a mixture of two or more of the 1,2-oxides. If desired, the initiator may be first oxyalkylated with one 1,2-oxide, followed by oxyalkylation with a different 1,2-oxide or a mixture of 1,2-oxides. The oxyalkylated initiator can be further oxyalkylated with a still different 1,2-oxide.

For convenience, “mixture,” when applied to a PAG containing a mixture of 1,2-oxides, includes both random and/or block polyethers such as those prepared by: (1) random addition obtained by simultaneously reacting two or more 1,2-oxides with the initiator; (2) block addition in which the initiator reacts first with one 1,2-oxide and then with a second 1,2-oxide, and (3) block addition in which the initiator first reacts with a first 1,2-oxide followed by random addition wherein the initiator reacts with a combination of the first 1,2-oxide and a second 1,2-oxide.

Any suitable ratio of different 1,2-oxides may be employed. When a mixture of propylene oxide (PO) with either ethylene oxide (EO) or butylene oxide (BO) is utilized to form polyethers by random and/or block addition, the proportion of PO may, in some embodiments, be between 40 weight percent and 60 weight percent, and preferably between 45 weight percent and 55 weight percent, based on total mixture weight.

Aliphatic alcohol reactants used in making the PAG include those containing one hydroxyl (OH) group and from 4 carbon atoms to 22 carbon atoms per molecule. Specific examples include, but are not limited to, butanol, pentanol, hexanol, neopentanol, isobutanol, decanol, propylene glycol n-butyl ether (available from The Dow Chemical Company as DOWANOL™ PnB), dipropylene glycol n-butyl ether (available from Dow as DOWANOL™ DPnB), and dodecyl alcohol (available e.g., as NACOL® 12-99 from Sasol).

PAGs of formula I contain a short alkyl group at the R¹ position. Such capping may be readily achieved by those skilled in the art, for instance by the Williamson Ether Synthesis. The uncapped PAG is first reacted with a base, converting the end OH groups into the alcoholate ion form. This alcoholate is then reacted with an alkyl halide, resulting in the capped PAG. Examples of the base that may be used are sodium hydroxide and sodium methanolate. An example of an alkyl halide that may be used is methyl chloride.

Preferred PAGs of formula I include materials of formula I-1, which are PAGs of formula I wherein R is linear C₄-C₁₄ alkyl. In some embodiments, R is linear C₄-₁₂ alkyl, alternatively it is C₄ alkyl, or alternatively C₁₂ alkyl.

Preferred PAGs of formula I and I-1 include materials of formula I-2, which are PAGs of formula I or I-1 wherein R¹ C₁-C₃ alkyl, alternatively R¹ is methyl.

Preferred PAGs of formula I, I-1 and 1-2 include materials of formula I-3, which are PAGs of formula I, I-1, or 1-2 wherein AO is a mixture of ethyleneoxy and propyleneoxy. In some embodiments, the proportion of propyleneoxy, based on the amount of PO used for making the PAG, is about 50 weight percent based on total mixture weight of ethyleneoxy and propyleneoxy.

Preferred PAGs of formula I, I-1 and I-2 include materials of formula I-4, which are PAGs of formula I, I-1, or 1-2 wherein AO is a mixture of propyleneoxy and butyleneoxy. In some embodiments, the proportion of propyleneoxy, based on the amount of PO used for making the PAG, is about 50 weight percent based on total mixture weight of butyleneoxy and propyleneoxy.

Preferred PAGs of formula I, I-1 and 1-2 include materials of formula I-5, which are PAGs of formula I, I-1, or 1-2 wherein AO is butyleneoxy.

Preferred PAGs of formula I, I-1 and 1-2 include materials of formula I-6, which are PAGs of formula I, I-1, or 1-2 wherein AO is propyleneoxy.

Preferred PAGs of formula I, I-1, 1-2, 1-3, 1-4, 1-5, and 1-6 include materials of formula I-7, which are PAGs of formula I, I-1, 1-2, 1-3, 1-4, 1-5, or 1-6 wherein the number average molecular weight is from 500 to 1500 g/mol. In some embodiments, the number average molecular weight may be 700 to 1300 g/mol, alternatively 800 to 1200 g/mol.

As noted above, compositions of the invention exhibit a favorable viscosity index (VI). VI indicates how a lubricant viscosity changes with temperature. For example, a low VI (e.g. 100) suggests that fluid viscosity will vary considerably when it is used to lubricate a piece of equipment that operates over a wide range of temperatures, such as from 20° C. to 100° C. As VI increases, lubricant performance also tends to improve. Based upon that recognition, skilled artisans prefer higher VI values (e.g. 150) over lower VI values (e.g. 100). Compositions of the invention have a viscosity index (VI) of 165 or more. In some embodiments, VI may be 180 or more, alternatively 200 or more, or alternatively 220 or more. In some embodiments, VI may be 400 or less.

To calculate VI, the kinematic viscosities, in centistokes (cSt) or its metric equivalent, square meters per second (m2/sec) at 40° C. and 100° C. are first measured using a Stabinger viscometer in accord with American Society for Testing and Materials (ASTM) D7042. The kinematic viscosities are then used to calculate a VI in accord with ASTM D2270.

Compositions of the invention possess favorable volatility profiles, as illustrated by their Noack volatilities. The more motor oils vaporize, the thicker and heavier they become, contributing to poor circulation, reduced fuel economy and increased oil consumption, wear and emissions. Lower volatilities are therefore generally preferred. The compositions of the invention have a Noack volatility of 13 percent or less. In some embodiments, the Noack volatility is 10 percent or less, alternatively 8 percent or less, or alternatively 6 percent or less. Noack volatility may be determined by ACEA's (European Automobile Manufacturers Association) test method CEC L-40, which determines the evaporation loss of lubricants in high-temperature service.

Some of the PAGs of formula I, particularly those in which the ethyleneoxy content is 0 weight percent may be oil soluble in hydrocarbon oils. Such materials are particularly advantageous because they facilitate replacement of mineral oils in engines with the PAG based materials. In particular, because of the oil solubility of the PAGs in mineral oil, the replacement can be easily carried out without the need for multiple flushing operations and associated waste disposal.

In some embodiments, the oil soluble PAGs of the preceding embodiment are of the formula II:

RO—(PO)_(n)—R¹  (II)

wherein R is C₄-C₂₂ alkyl; PO is propyleneoxy; n is 8-16; and R¹ is C₁-C₃ alkyl.

Preferred oil soluble PAGs of formula II include materials of formula II-1, which are PAGs of formula II wherein R is linear C₄-C₁₄ alkyl. In some embodiments, R is linear C₄-12 alkyl, alternatively C₄ alkyl, or alternatively C₁₂ alkyl.

Preferred oil soluble PAGs of formula II and II-1 include materials of formula II-2, which are PAGs of formula II or II-1 wherein R¹ is methyl.

Preferred oil soluble PAGs of formula II, II-1, and 11-2 include materials of formula II-3, which are PAGs of formula II, II-1, or II-2 wherein the number average molecular weight is from 500 to 1500 g/mol. In some embodiments, the number average molecular weight may be 700 to 1300 g/mol, alternatively 800 to 1200 g/mol.

In addition to the PAGs as described above, the compositions of the invention also contain an additive package comprising an anti-oxidant. The additive package may further contain additional additives commonly used in the industry, for instance, an extreme pressure anti-wear additive, or an anti-corrosion additive, or a friction modifier, or an acid scavenger, or any combination of the foregoing. In some embodiments, the additive package contains all of the foregoing components, i.e., an anti-oxidant, an extreme pressure anti-wear additive, an anti-corrosion additive, a friction modifier, and an acid scavenger.

The antioxidant may be any such conventional material. The antioxidant may vary widely, including compounds from classes such as amines and phenolics. The antioxidant may include a sterically hindered phenolic antioxidant (for example, an ortho-alkylated phenolic compound such as 2,6-di-tert-butylphenol, 4-methyl-2,6-di-tert-butylphenol, 2,4,6-tri-tert-butylphenol, 2-tert-butylphenol, 2,6-di-isopropylphenol, 2-methyl-6-tert-butylphenol, 2,4-dimethyl-6-tert-butylphenol, 4-(N,N-dimethylaminomethyl)-2,6-di-tert-butylphenol, 4-ethyl-2,6-di-tert-butylphenol, 2-methyl-6-styrylphenol, 2,6-di-styryl-4-nonylphenol, and their analogs and homologs).

Representative examples of suitable antioxidants also include, but are not limited to, IRGANOX™ L01, L06, L57, L93 (alkylated diphenyl amines and alkylated phenyl-naphtyl amines); IRGANOX™ L101, L107, L109, L115, L118, L135 (hindered phenolic antioxidants); IRGANOX™ L64, L74, L94, L134, and L150 (antioxidant blends); IRGAFOS™ 168 (di-tert-butyl phenyl phosphate); IRGANOX™ E201 (alpha-tocopherol), and IRGANOX™ L93 (sulfur-containing aromatic amine antioxidant).

Representative examples of preferred antioxidants include, but are not limited to, amine antioxidants such as N-phenyl-1-naphthalenamine, N-phenylbenzenamine reaction products with 2,4,4-trimethylpentenes; phenothiazine; dibenzo-1,4,thiazine; 1,2-dihydroquinoline; poly(2,2,4-trimethyl-1,2-dihydroquinoline); and 6,6′-di-tert-butyl-2,2′-methylendi-p-cresol.

The lubricant composition preferably contains from 0.01 wt percent to 1.0 wt percent, more preferably from 0.05 wt percent to 0.7 wt percent, of such antioxidant(s), each wt percent being based on total lubricant composition weight.

The extreme pressure and anti-wear additives can be any such conventional material. Representative examples of extreme pressure and anti-wear additives include, but are not limited to, dialkyl-dithio-carbamates of metals and methylene, esters of polyaspartic acid, triphenyl-thio-phosphates, diaryldisulfides, dialkyldisulfides, alkylarylsulfides, dibenzyldisulphide, and combinations thereof. Representative examples of preferred extreme pressure and anti-wear additives include, but are not limited to, dibenzyldisulfide, O,O,O-triphenylphosphorothioate, Zn-di-n-butyldithiocarbamate, Mo-dibutyldithiocarbamate, and Zn-methylene-bis-dialkyldithiocarbamate, with dibenzyldisulfide being especially preferred. Representative examples of commercially available anti-wear additives that can be employed in the practice of this invention include but are not limited to IRGALUBE™ 63, 211, 232, and 353 (isopropylated triaryl phosphates); IRGALUBE™ 211 and 232 (nonylated triphenyl phosphorothionates); IRGALUBE™ 349 (amine phosphate); IRGALUBE™ 353 (dithiophosphate); IRGAFOSTM DDPP (iso-decyl diphenyl phosphite); and IRGAFOS™ OPH (di-n-octyl-phosphite).

The anti-corrosion additive (also known as a “metal deactivator”) may be any single compound or mixture of compounds that inhibits corrosion of metallic surfaces. The corrosion inhibitor can be any such conventional material. Representative anti-corrosion additives include thiadiazoles and triazoles such as tolyltriazole; dimer and trimer acids such as those produced from tall oil fatty acids, oleic acid, and linoleic acid; alkenyl succinic acid and alkenyl succinic anhydride corrosion inhibitors such as tetrapropenylsuccinic acid, tetrapropenylsuccinic anhydride, dodecenylsuccinic acid, dodecenylsuccinic anhydride, hexadecenylsuccinic acid, and similar compounds; and half esters of C₈-C₂₄ alkenyl succinic acids with alcohols such as diols and polyglycols. Also useful are aminosuccinic acids or derivatives thereof. Preferred anti-corrosion additives include, but are not limited to, morpholine, N-methyl morpholine, N-ethyl morpholine, amino ethyl piperazine, monoethanol amine, 2 amino-2-methylpropanol (AMP), liquid tolutriazol derivatives such as 2,2′-methyl-1H-benzotriazol-1-yl-methyl-imino-bis and methyl-1H-benzotriazol, isopropyl hydroxylamine, IRGAMET™ 30 (liquid tolutriazol derivative), IRGAMET™ 30 (liquid triazol derivative), IRGAMET™ SBT 75 (tetrahydrobenzotriazole), IRGAMET™ 42 (tolutirazole derivative), IRGAMET™ BTZ (benzotriazole), IRGAMET™ TTZ (tolutriazole), imidazoline and its derivatives, IRGACOR™ DC11 (undecanedioic acid), IRGACOR™ DC 12 (dodecanedioic acid), IRGACOR™ L 184 (TEA neutralized polycarboxylic acid), IRGACOR™ L 190 (polycarboxylic acid), IRGACOR™ L12 (succinic acid ester), IRGACOR™ DSS G (n-oleyl sarcosine), and IRGACOR™ NPA (iso-nonyl phenoxy acetic acid). The lubricant composition preferably contains from 0.005 wt percent to 0.5 wt percent, and more preferably from 0.01 wt percent to 0.2 wt percent, of anti-corrosion additive, each wt percent being based upon total lubricant composition weight.

The acid scavenger is a single compound or a mixture of compounds that has an ability to scavenge acids. The acid scavenger can be any such conventional material. Representative acid scavengers include, but are not limited to, sterically hindered carbo-diimides, such as those disclosed in FR 2,792,326, incorporated herein by reference. The lubricant composition preferably contains from 0.1 wt percent to 1 wt percent of the acid scavenger, based upon total lubricant composition weight.

The friction (rheology) modifier can be any such conventional material. A representative non-limiting example of such a material is a copolymer of diphenylmethane-diisocyanate hexamethylene diamine and sterarylamine (for example, LUVODUR™ PVU-A). The lubricating compositions preferably contain from 0.01 wt percent to 1.0 wt percent, more preferably from 0.05 wt percent to 0.7 wt percent, of such friction modifiers, each wt percent being based on total lubricant composition weight.

The lubricant compositions optionally contain small amounts of a demulsifier and/or an antifoam agent. Such demulsifiers include organic sulphonates and oxyalkylated phenolic resins. Various antifoam agents are well known in the art, such as stearylamine, silicones and organic polymers such as acrylate polymers. If present, such additives typically comprise, on an individual basis, no more than 1 wt percent based on total lubricant composition weight. The lubricant compositions also optionally contain a thickening agent such as a polyethylene oxide, a polyacrylate, a styrene-acrylate latex, a styrene butadiene latex, and a polyurethane prepolymer. The thickening agent when present, is used in an amount sufficient to further provide the lubricant composition with a desired thickness or viscosity. The compositions may also contain a dispersant system to stabilize products from the combustion process.

In some embodiments, the lubricant composition contains less than 0.1 weight percent, alternatively less than 0.05 weight percent, of aspartic acid or an aspartic acid derivative (which may function as an acid scavenger). In some embodiments, the lubricant composition contains no aspartic acid or its derivatives.

In some embodiments, the lubricant composition of the invention may comprise from 50 to 99.9 weight percent of the PAG based on the total weight of the composition. In some embodiments, the composition comprises from 0.10 to 10 weight percent of the additives package based on the total weight of the composition.

The lubricant compositions may be prepared by simple addition of the components and mixing. This can occur at room temperature (nominally 25° C.). Higher temperatures of up to, for example, 170° C., may be employed to effect solubilization of the additives into the PAG base stock. One may effect mixing, for instance, ultrasonically or by using a high speed dispergator.

The compositions have utility as lubricants for instance in internal combustion engines, such as automobile engines. Thus, in some embodiments, the lubricant composition is a motor oil. Further, in some embodiments, the motor oil is 0W-20 motor oil.

As used in this specification, ethyleneoxy refers to —CH₂—CH₂—O—, propyleneoxy refers to —CH₂—CH(CH₃)—O— or —CH(CH₃)—CH₂—O—, and butyleneoxy refers to —CH₂—CH(CH₂CH₃)—O— or —CH(CH₂CH₃)—CH₂—O—.

The term “alkyl” encompasses straight and branched chain aliphatic groups having the indicated number of carbon atoms.

Numeric ranges are inclusive of the numbers defining the range. Unless otherwise indicated, ratios, percentages, parts, and the like used herein are by weight.

The following examples are illustrative of the invention but are not intended to limit its scope.

EXAMPLES

Materials used in the examples are shown in Table 1. PAGs may be prepared as described above. For instance, the PAG of Sample A is dipropylene glycol n-butyl ether started EO-PO (1:1) random copolymer with a molecular weight of 800 g/mol, methyl capped.

TABLE 1 Mw Sample (g/mol) Initiator Oxide Cap (R¹) Formulated⁴ A 800 DPnB¹ EO/PO (1:1) methyl yes B 900 DPnB PO methyl no C 850 Nacol 12-99² PO methyl no D 800 PnB³ BO methyl no E 1200 Nacol 12-99 PO/BO (1:1) methyl no F 800 Nacol 12-99 PO methyl no G 800 DPnB PO/BO (1:1) methyl yes H 800 DPnB BO methyl yes ¹DPnB is dipropylene glycol n-butyl ether; ²Nacol 12-99 is a 12 carbon linear fatty alcohol; ³PnB is propylene glycol n-butyl ether; ⁴Indicates if PAG is formulated with an additive package containing 0.5% of an anti-oxidant, such as N-phenyl-1-naphthalenamine, IRGANOX L57, 6,6′-di-tert-butyl-2,2′-methylendi-p-cresol, or phenothiazine.

Example 1 Viscosity Index

Table 2 shows the viscosity index (VI) of various samples.

TABLE 2 Sample VI A 230 B 224 C 227 D 173 E 196 F 220 G 191 H 169

Example 2 Noack Volatility

Table 3 compares Noack volatility between formulated and unformulated samples.

TABLE 3 Volatility Loss Pass/fail CEC-L- Sample NOACK CEC L-40 40-A93 limits¹ A (formulated) 9 pass B 29 fail C fail D 27 fail E fail F fail G (formulated) 6.5 pass H (formulated) 5.6 pass ¹Indicates whether the composition passes or fails ACEA's (European Automobile Manufacturers Association) CEC-L-40-A93 test under limits A3 A3/B3 - A3/B4 - A5/B5. A pass under these limits requires an evaporative loss of 13% or less under the tested conditions.

The data in Table 3 shows that formulated samples (i.e., inventive samples A, G, and H) exhibit excellent Noack volatility and pass the indicated ACEA test. In contrast, the unformulated samples (i.e., comparative samples B, C, D, E, F) fail the ACEA test. 

What is claimed is:
 1. A lubricant composition comprising: (a) a polyalkylene glycol of formula I: RO—(AO)_(n)—R¹  (I) wherein R is C₄-C₂₂ alkyl; AO is independently ethyleneoxy, propyleneoxy, butyleneoxy, or mixtures of two or more thereof; n is 8-16; and R¹ is C₁-C₆ alkyl; and (b) an additive package comprising an amine anti-oxidant, wherein the lubricant composition has a Noack volatility of 13 percent or less and a viscosity index of at least
 165. 2. The lubricant composition according to claim 1 wherein R is linear C₄-C₁₄ alkyl
 3. The lubricant composition according to claim 1 wherein R¹ is C₁-C₃ alkyl.
 4. The lubricant composition according to claim 1 wherein the polyalkylene glycol of formula I has a number average molecular weight of from 500 to 1500 g/mol.
 5. The lubricant composition according to claim 1 having a viscosity index of at least
 180. 6. The lubricant composition according to claim 1 wherein AO is a mixture of ethyleneoxy and propyleneoxy.
 7. The lubricant composition according to claim 1 wherein AO is a mixture of propyleneoxy and butyleneoxy.
 8. The lubricant composition according to claim 1 wherein AO is butyleneoxy.
 9. The lubricant composition according to claim 1 wherein the polyalkylene glycol is of formula II: RO—(PO)_(n)—R¹  (II) wherein R is C₄-C₂₂ alkyl; PO is propyleneoxy; n is 8-16; and R¹ is C₁-C₃ alkyl.
 10. The lubricant composition according to claim 1 that the additive package further comprises: (i) an extreme pressure anti-wear additive, or (ii) an anti-corrosion additive, or (iii) a friction modifier, or (iv) an acid scavenger, or (v) any combination of (i)-(iv).
 11. The lubricant composition according to claim 1 that is a motor oil.
 12. The lubricant composition according to claim 11 wherein the motor oil is 0W-20 motor oil.
 13. A method of lubricating an internal combustion engine, comprising providing a lubricant composition according to claim
 1. 